Method of utilising waste heat in turbocharger unit of an internal combustion engine and internal combustion engine arrangement

ABSTRACT

Method of utilizing waste heat in a turbocharger unit of an internal combustion engine unit having means for recovering heat from the combustion process, the engine unit comprising a turbocharger unit adapted to feed pressurized combustion air to the engine and to receive exhaust gases from the engine, wherein the means for recovering heat is producing steam, which is generated using waste heat from the engine and wherein the steam is injected to the turbocharger unit and the energy of steam is at least partially recovered in the turbocharger. The invention relates also to an internal combustion engine arrangement which comprises means for recovering heat from the combustion process and a turbocharger unit adapted to feed pressurized combustion air to the engine and to receive exhaust gases from the engine. The turbocharger unit is provided with a steam injection arrangement connected with the means for recovering heat.

TECHNICAL FIELD

[0001] Invention relates to method of utilising waste heat inturbocharger unit of an internal combustion engine unit having means forrecovering heat from the combustion process, the engine unit comprisinga turbocharger unit adapted to feed pressurised combustion air to theengine and to receive exhaust gases from the engine according topreamble of claim 1. Invention relates also to internal combustionengine comprising means for recovering heat from the combustion process,a turbocharger unit adapted to feed pressurised combustion air to theengine and to receive exhaust gases from the engine according topreamble of claim 11.

BACKGROUND ART

[0002] Different systems for utilisation of waste heat of an internalcombustion engines are known. The most commonly used solution is a socalled combined cycle, where the waste heat of internal combustionengine is utilised in a separate steam engine. An example of such asolution is provided for instance in publication U.S. Pat. No.5,133,298. This kind of solution is a relatively expensive and somewhatdifficult also, as internal combustion engines differ strongly in sizeand each size range requires a different steam engine.

[0003] In number of patents, for instance in U.S. Pat. No. 4,377,934,U.S. Pat. No. 4,406,127, U.S. Pat. No. 4,706,468 and U.S. Pat. No.4,901,531, different versions of the bottom steam cycle are proposed, inwhich at least one cylinder of the internal combustion engine is used asthe steam power recovery device, which in fact is a modification of theclassic combined cycle engines. In U.S. Pat. No. 4,433,548 thealternating use of same cylinders for combustion and steam power strokesis described. Further, in U.S. Pat. No. 4,409,932 injection of the steamduring the power stroke i.e. after combustion is proposed in a petrolcar engine. A negative feature of all these solutions is that theemissions of the combined systems are the same as for the internalcombustion (top) engine.

[0004] Many publications, for example U.S. Pat. No. 3,761,019, U.S.4,014,299, U.S. Pat. No. 4,027,630, U.S. Pat. No. 4,059,078, U.S. Pat.No. 4,391,229, U.S. Pat. No. 4,409,931 and U.S. Pat. No. 4,844,028,describe steam injection into an inlet manifold of engines to controlpower, knock or NOx-emissions. However, these solutions using low gradesteam and leaving the energy transformations out of considerations, donot necessarily provide increased efficiency.

[0005] Use of steam to supercharge the engine is proposed inpublications U.S. Pat. No. 3,948,235 and U.S. Pat. No. 4,913,098. In thepublication U.S. Pat. No. 3,948,235 a special steam turbine driving aseparate compressor is described to achieve higher supercharge levels,whereas in the U.S. Pat. No. 4,913,098 a steam ejector located in theinlet manifold is proposed for the same purpose. However, developing aspecial turbine and compressor for an internal combustion engine is evenmore difficult than just developing a steam turbine for producing shaftpower or electrical power, as it is done in the classic combined powerplants. And, using steam ejectors leads to very large energy losses,which make the system unattractive. This is because to utilise the wasteheat of an internal combustion engine with minimal water usage the steamparameters—pressures and temperatures—must be very high leading toextreme steam injection speeds and thus losses in an ejector. The lossesin an ejector are considerable in systems with large velocity gradientsdue turbulence generation i.e. aerodynamic friction. The losses can bereduced by aerodynamically proper design to a level of about 30% butthis is not a practical solution due to costs of development of such aturbo-machine.

[0006] Turbochargers as such are developed to achieve high conversionefficiency of the exhaust gas energy into the energy of compressed airused in the engine. Total energy conversion efficiencies of modernturbocharger approach 70%. Typically few turbocharger families areavailable to cover the possible engine applications and thusturbochargers able to accommodate more energy are readily available assuch.

DISCLOSURE OF THE INVENTION

[0007] An object of the present invention is to provide a method inwhich the shortcomings of prior art solutions have been minimised. It isalso an object of the present invention to provide a method of utilisingwaste heat in a turbocharger unit of an internal combustion engine unit.Particularly an object of the present invention is to achieve themaximum charging pressures in simple way in particular by using amodified turbocharger accommodating both steam and air.

[0008] Objects of the invention may by achieved by method of utilisingwaste heat according to claim 1 and by internal combustion engineaccording to claim 11. Preferred or optional features of the inventionare defined by the dependent claims.

[0009] According to the invention the method of utilising waste heat inturbocharger unit of an internal combustion comprises mainly as follows.The engine unit has means for recovering heat from the combustionprocess, and comprises a turbocharger unit adapted to feed pressurisedcombustion air to the engine and to receive exhaust gases from theengine. In the method the means for recovering heat is producing steam,which is generated using waste heat from the engine and the steam isinjected to the turbocharger unit. The internal combustion enginearrangement comprises means for recovering heat from the combustionprocess, a turbocharger unit adapted to feed pressurised combustion airto the engine and to receive exhaust gases from the engine. Theturbocharger unit is provided with steam injection arrangement connectedwith the means for recovering heat. Thus, the energy of steam is atleast partially recovered in the turbocharger. This way it is possibleto minimise NOx- emissions and enhance the power output of the engine.

[0010] According to an aspect of the invention the steam is injectedinto the high-pressure region of turbine of the turbocharger unit bymeans of the steam injection arrangement provided in the high-pressureregion of turbine of the turbocharger unit. This manner mixing of steamwith the exhaust gases is minimised and the steam energy is recovered inthe turbine.

[0011] According to another aspect of the invention the steam isinjected into the compressor or the turbocharger though a steaminjection arrangement provided in the compressor of the turbocharger.The steam is preferably injected to the tip -section of the impeller ofthe compressor through a number of nozzles so that a considerableportion of the steam energy is used to drive the impeller. Preferably asupersonic nozzle is used for the steam injection. The steam may also beinjected tangentially into inlet of the compressor close to the impellerso that mixing of steam with the air is minimised before the impeller,and causing steam layer to rotate and to drive the impeller. It is alsopossible, and in some cases even desirable, to have the steam injectedsimultaneously into both the high-pressure region of the turbine andinto the compressor of the turbo-charger, whereas both the compressorand turbine of the turbo-charger unit are provided with steam injectionarrangement.

[0012] The steam injection rate is preferably controlled by a closedloop control system, which controls the injection rate so as to keep thetemperature of the exhaust gases at a pre-set level. The steam rate mayalso be controlled so that transient operation of turbocharger isenhanced.

[0013] According to the invention the fact that there are commerciallyavailable turbochargers to cover possible engine applications is takeninto consideration. Modifying an existing turbocharger to utiliseefficiently the energy of steam generated using the waste heat of theengine is a preferred starting point of the invention. Both the inletair heat and engine cooling heat as well as the exhaust heat may beadvantageously used to generate the steam. Taking into account theenergy balance of the engine, this means that a quantity of waterapproximately 3-4 times the quantity of fuel used by the engine can beconverted into high grade superheated steam having pressure up to 220bar and temperatures up to 850 K. Preferably the mass of the steam isbetween 10 to 20% of the mass of the air depending on the fuel/airequivalence ratio of the engine and thus no radical changes in theturbocharger are needed to utilise the steam energy.

[0014] The injection into the turbine is optimal for one aspect of theinvention, which is to provide means to increase the power output andefficiency of the engine. The injection of the steam into the compressorprovides, in addition to increasing the pressure, means to substantiallyreduce the nitrogen oxide emissions. An additional benefit of theinvention is also that the steam injection may be used to reducepossible turbocharger lag during transient operation of the engine andto control the charging pressure in order to obtain a favourable torquecurve of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A full understanding of the present invention may be gained byreference to the following detailed description when read in conjunctionwith the accompanying drawings, wherein:

[0016]FIG. 1 shows the maximum conversion efficiency of waste heat of anideal cycle into steam energy available for utilisation as a function ofpressure for different temperatures.

[0017]FIG. 2 is a schematic illustration of an internal combustionsystem with turbocharger unit according to the invention,

[0018]FIG. 3 is a schematic drawing of a system based on steam injectioninto the turbine of the turbocharger.

[0019]FIG. 4 is a schematic drawing of a system based on steam injectionat the tip of the impeller of the compressor of the turbocharger.

[0020]FIG. 5 is a schematic representation of the steam injection at theinlet to the compressor of the turbocharger.

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] Typically 30-40% of the fuel energy leaves an internal combustionengine in form of recoverable waste heat. The waste heat to be convertedinto mechanical energy must go through a thermodynamic cycle. If steamis used as the working fluid for that cycle then the maximum possibleefficiency is achieved in an ideal Clausius-Rankine cycle, which ispresented in FIG. 1. The efficiency of this cycle is shown in verticalaxis 19 of FIG. 1 as a function of pressure, which is shown inhorizontal axis 18. The presentation is assuming surrounding pressure of1 bar, and showing three temperatures 500° C., curve 22, 400° C., curve21, and saturated vapour temperature for the respective pressure, curve20, which is the lowest possible temperature for proper functioning ofsteam engine. The saturation temperature changes approximately linearlyfrom 100° C., at 1 bar to 374,15° C. at 220,8 bar, which is the criticalpoint. As it can be seen from FIG. 1 high pressures and temperaturesoffer the best efficiency. The efficiency drops rapidly with pressurebelow 50 bar, which is thus the lowest pressure for practicalapplication of steam cycle.

[0022] According to the invention a turbocharger of an engine isutilised as will be described below. This is possible because it hasbeen noticed that the mass of the steam needed is typicallysubstantially below 20% of the mass of air and thus it can beaccommodated by the turbocharger or a slightly larger member of theturbocharger family used for the engine.

[0023] In FIG. 2 there is schematically shown an internal combustionsystem with turbocharger unit according to the invention. The internalcombustion system comprises a combustion engine 23, which is here areciprocating combustion engine. It is provided with an inlet manifold25 for combustion air and outlet manifold 24 for exhaust gases beingconnected to the turbocharger unit 17. Steam 14 is produced by a steamgenerator 26,26′ utilising the waste heat of the engine. This may beoriginating from e.g. from cylinder cooling 26 and/or from hot exhaustgases 26′ and/or inlet air cooling (not shown). The steam is fed bymeans of a control unit 29 into the compressor and/or turbine of theturbocharger by supply lines 27,28. The total steam injection rate iscontrolled by preferably maintaining the temperature of the exhaustgases at pre-selected level, which is advantageously below dew pointtemperature. In order to provide continues control over the steaminjection the exhaust gas temperature is measured by probe 30 shown inFIG. 2. Since the temperature of the exhaust gases is an easilymeasurable quantity a closed loop. control unit 29 of steam injectionrate control system based on exhaust temperature is advantageouslyapplied in the system.

[0024] Efficient utilisation of the steam energy requires minimisationof the steam-gas mixing losses. This in turn may be accomplished byinjection of the steam into a high pressure, high velocity zone of theturbocharger and extracting energy from the high velocity steam jet toslow it down as much as possible before mixing with the rest of the gas.This is achieved according to the present invention by arrangement shownin FIG. 3. The steam 14 is here injected into the high-pressure part ofthe turbine through a supersonic De Laval nozzle 1 parallel to theexhaust gas 16. The injection is performed in such a way that mixing isminimised. This may be accomplished by the splitter plate 2 provided inconnection with the turbine inlet. Thus the steam energy is efficientlyutilised due to further expansion in the turbine nozzle 3 and impeller4. More energy is thus transferred to the shaft of the turbocharger andhigher pressure is available in the inlet manifold of the engine.

[0025] The higher pressure in turn is utilised during the intake strokeof the engine to produce shaft power. An estimate of the losses showsthat about 50% of the available steam energy can be utilised using theabove method.

[0026] Utilisation of the steam for dilution of the charge to reduce NOxemissions requires injection of the steam into the inlet of the engine.This can be achieved with minimal energy losses according to theinvention by injecting the steam into the high-pressure part of thecompressor so that the steam will drive the impeller. This will reducethe speed of the steam jet and increase the air pressure. The optimalsolution for this case is shown schematically in FIG. 4. Steam 14 iscollected here in a collector chamber 5 and is distributed to severalsmall supersonic nozzles 6. The steam jets formed are thus driving theimpeller 7 of the compressor. Several nozzles are used in this case tominimise the flow perturbations in the compressor and the non-stationaryaerodynamic forces on the blades of the impeller. The number andinclination angles of the nozzles may be optimised experimentally toobtain the best effects for each respective case. About 40% of thecompressed air energy could be recovered in this kind of systems.

[0027] Another system is shown in FIG. 5. The steam is introducedtangentially through the tube 8 into a steam scroll 9 and injectedthrough the nozzle 10 into the inlet of the compressor forming a walljet 12. This minimises the mixing of the steam with the incoming air 11.The rapidly rotating steam layer drives the impeller 13 and thus thesteam energy is recovered, and the speed of steam reduced. While beingsimpler, this embodiment may not be as efficient as the one shown inFIG. 4.

[0028] As much as possible of the waste heat of the engine should berecovered in the steam system for best efficiency. However, at the sametime the temperature of the exhaust gases must be higher than a minimalvalue to avoid condensation in the outlet system and related corrosion.This is particularly important where high sulphur contents fuel is usedin the engine and, also to provide buoyancy for better dispersion of theexhaust gases in the atmosphere. Therefore, the injection rate of thesteam shall be limited by the exhaust gas dew point temperature.

[0029] While specific embodiments of the invention and descriptions ofits utilisation to raise the power and efficiency of the engine andreduce pollutant emissions are described herein, it shall be understoodby those skilled in the art, that other embodiments and alternativescould be employed in light of the overall teaching of the disclosure. Inparticular a combination of the steam injection methods may beadvantageously employed. The invention is thus not limited to theembodiments and numerical values shown but several modifications of theinvention are reasonable within the scope of the attached claims.

1. Method of utilising waste heat in turbocharger unit of an internalcombustion engine (23) unit, in which heat from the combustion processis recovered by a steam generator (26,26′), and in which the engine unitcomprising a turbocharger unit (17) which feeds pressurised combustionair (15) to the engine and receives exhaust gases (16) from the engine,characterised in that steam (14) generated in the steam generator(26,26′) using waste heat from the engine is injected to theturbocharger unit (17) via a steam injection arrangement provided in theturbocharger unit (17).
 2. Method according to claim 1, characterised inthat the steam (14) is injected (28) into the high-pressure region ofturbine of the turbocharger unit (17) so that mixing of steam with theexhaust gases is minimised and the steam energy is recovered in theturbine.
 3. Method according to claim 1, characterised in that the steamis injected (27) into the compressor of the turbocharger (17).
 4. Methodaccording to claim 3, characterised in that the steam is injected to thetip -section of the impeller (13) of the compressor through a number ofnozzles (6) so that a considerable portion of the steam energy is usedto drive the impeller.
 5. Method according to claim 3, characterised inthat the steam is injected tangentially (12) into inlet of thecompressor close to the impeller (13) so that mixing of steam with theair is minimised before the impeller, and causing steam layer rotatingand driving the impeller.
 6. Method according to claim 2 or 3,characterised in that the steam (14) is injected through a supersonicnozzle (1).
 7. Method according to claim 1, characterised in that steamis injected into both the high-pressure region of the turbine and intothe compressor of the turbocharger (17).
 8. Method according any ofpreceding claims, characterised in that the steam injection rate iscontrolled by a closed loop control system (29,30) keeping thetemperature (30) of the exhaust gases at a pre-set level.
 9. Methodaccording any of preceding claims, characterised in that the mass of thesteam (14) is between 10 to 20% of the mass of combustion air (15). 10.Method according to claim 1, characterised in that the energy of steamis at least partially recovered in the turbocharger.
 11. Internalcombustion engine (23) arrangement comprising means for recovering heatfrom the combustion process in a form of a steam generator (26,26′), aturbocharger unit (17) adapted to feed pressurised combustion air (15)to the engine and to receive exhaust gases (16) from the engine,characterised in that the turbocharger unit (17) is provided with steaminjection arrangement (14) connected with the steam generator (26,26′).12. Internal combustion engine according to claim 11, characterised inthat that the steam injection arrangement (14) is provided in thehigh-pressure region of turbine of the turbocharger unit (17). 13.Internal combustion engine according to claim 11, characterised in thatthat the steam injection arrangement (14) is provided in the compressorof the turbocharger (17).
 14. Internal combustion engine according toclaim 11, characterised in that that the steam injection arrangement(14) is provided in the compressor of the turbocharger (17) and in thehigh-pressure region of turbine of the turbocharger unit (17).